1. Technical Field of the Invention
The present invention relates to a hydraulic pressure driving work machine such as a backhoe or the like attached on a swiveling work vehicle or the like. More particularly, it relates to a piping structure of operation oil hoses for supplying operation oil to hydraulic actuators for driving respective drive parts of the work machine, and relates to a reinforcement structure of a boom which is one of the drive parts thereof.
2. Description of the Related Art
There is a well known work machine such as backhoe or the like which comprise a combination of drive parts such as a boom, an arm and a work attachment (a bucket or the like), each of which are individually driven with a hydraulic actuator. Such a work machine is attached, for example, on a turntable mounted above a running machine of a swiveling type vehicle or on either a front end or a rear end or the like of a tractor, wherein operation oil hoses are extended to the hydraulic actuators for driving the respective drive parts from a hydraulic pressure controller arranged on a main body of the vehicle.
These operation oil hoses are conventionally arranged from a base end of the boom to a tip end thereof along a rear surface of the boom whose base end is vertically rotatably attached on a main body of a vehicle such as a turntable or the like (normally, via a hinge member referred to as a boom bracket) to be extended to each of the hydraulic actuators. Via the hose guide member arranged in the vicinity of the base end of the rear surface of the boom, the operation oil hoses are guided to the rear surface of the boom. In addition, at the rear of the hose guide member (a vehicle side portion), a definite space is provided so that a deflection space of the operation oil hoses can be allowed.
It is hard to say that the operation oil hoses are favorably protected in its piping structure because the operation oil hoses are exposed to the rear surface of the boom. In addition, in a vehicle structure in which driver's room (a cab) is arranged at the rear of the boom, the rearward rotation region of the boom is restricted (namely, a rise angle is restricted). Furthermore, in order to secure the deflection space of the operation oil hoses, the boom bracket must be arranged at a location shifted to the work attachment to some degree from the vehicle body. On the whole, the center of gravity of the work machine is shifted to the work attachment so as to be separated away from the position of the center of gravity of the vehicle body, whereby the stability is unfavorable. Furthermore, if the vehicle is the swiveling type vehicle, the swivel radius at work becomes large so as to make a work at a narrow place difficult.
In addition, the hydraulic actuator (for example, a bucket cylinder) for the work attachment (for example, a bucket) is arranged beside the arm, and the operation oil hoses to the hydraulic actuator must be provided on the periphery of the pivot portion of the base end of the arm onto the tip end of the boom with a deflection space which is secured following the rotation operation of the arm with respect to the boom. However, since the operation oil hoses are arranged up to the vicinity of the tip end of the rear surface of the boom, the bending degree becomes large as the arm is rotated away from the boom, thereby causing the life of the operation oil hose to be short.
Incidentally, with respect to the operation oil hoses connected to the hydraulic actuator for the arm or the work attachment, there can be seen a structure such that the boom is formed, for example, in an H-shaped cross section or a U-shaped cross section from a bent intermediate portion thereof up to the tip end portion thereof and an operation oil hose is arranged inside of the boom, namely, between both side plates of the boom. In this structure, the base end portion of the actuator (an arm cylinder) for driving the arm can be arranged inside of the boom. Therefore, the operation oil hoses and the base end of the arm cylinder do not project at the rear of the boom, thereby enabling the rearward rotation angle of the boom to be set to a large level to some extent, and being protected both the side plates and belly plates of the boom.
However, in order to facilitate the connection of the operation oil hoses and the maintenance thereof, or to secure the deflection space, between the intermediate portion and the tip end portion of the boom, the rear surface thereof must be formed into an open configuration (namely, an H-shaped cross section, a U-shaped cross section or the like). Such structure can be applied only to a small type work machine with a small capacity because the strength of the boom is not so high. In order to assume a structure such that the operation oil hoses are piped into the boom while the rear surface of the boom being covered, a structure must be secured such that the hoses can be easily connected to the hydraulic actuator and conducted and can be provided with a sufficient deflection space.
Furthermore, the hydraulic actuator (a boom cylinder) for driving the boom is normally arranged on the belly side of the boom and the base end of the actuator is pivoted on a foremost end portion of the boom bracket facing toward the work attachment. In such a state, the operation oil hoses for the boom cylinder extended from the turntable require a larger deflection around the pivoting portion of the base end of the boom when an attempt is made to pipe the operation oil hose in the vicinity of the boom bracket. Consequently, the operation oil hoses are usually piped so as to pass outsides of the boom, whereby the piping is exposed and remains unprotected which also appears visually unfavorable.
Next, referring to a reinforcement structure which is conventionally seen particularly in the boom, the support portion on the base end of the boom to be pivoted onto the boom bracket is constituted with casting material because a large load is inflicted thereon, and the support portion is joined by welding or the like to the main body of the boom, and a reinforcing plate is plastered on the joint portion to secure the strength. Consequently, a part of the reinforcing plate comes into contact with the casting support portion while the other part of the remaining part comes into contact with the steel-plate made main body of the boom. However, the conventional reinforcing plate is formed in a constant thickness so as to apply a uniform stress over the boom through its whole surface. Since the thickness of the reinforcing plate is set so that a load is inflicted upon the casting support portion, a relatively strong stress is applied to the relatively weak steel plate serving as the main body of the boom. This is not preferable in structure.
Furthermore, on the tip end portion of the boom is fixed an arm fulcrum bracket for pivoting the arm. A portion of the arm fulcrum bracket which projects from the tip end of the main body of the boom has a definite thickness so as to endure the support of the base end of the arm. When the arm fulcrum bracket is joined to the main body of the boom with this thickness, a stress is concentrated upon the main body of the boom. Consequently, a surfacing process is provided on the arm fulcrum bracket with a milling cutter or the like so as to require a large number of manpower and high cost.